That is the correct string for the radeon OpenGL renderer. If you are running Unity (or Compiz in general), make sure that "Undirect Fullscreen Windows" is checked to get the best performance in full-screen games. (Although the feature was introduced in Ubuntu 12.10, it has been backported to Ubuntu 12.04.2 - its just not default in 12.04.)

Unfortunately the 3D performance of Radeon and Nouveau is not quite up-to-par. Their 2D performance is fantastic, but the drivers are not well optimized at the moment. The Intel graphics driver is much better optimized, but the hardware performance is lacking. I'm hoping that the open-source driver AMD recently released for the Radeon HD 8000 series is a game changer when the hardware arrives!

That said, I am able to run Nexuiz, Minecraft, and Team Fortress 2 acceptably on my Radeon HD 5770 using Radeon and Gallium 0.4.